Device for sensing a magnetic field, magnetic field meter and an ammeter

ABSTRACT

Proposed are a device, a magnetic-field sensor and a current sensor, the device having the feature that provision is made for a first magnetic-field sensing means, for a second magnetic-field sensing means, and for a third magnetic-field sensing means, a first output variable of the first magnetic-field sensing means being provided as a first input variable, a second output variable of the first magnetic-field sensing means being provided as a second input variable, the first input variable being provided as input variable for the second magnetic-field sensing means, and the second input variable being provided as input variable for the third magnetic-field sensing means.

BACKGROUND INFORMATION

The number of application ranges for magnetic-field sensors isincreasingly growing, in particular, in the automotive sector. Magneticfield sensing can be used, inter alia, for non-contact, low-loss andfloating measurement of currents. Examples are the determination ofelectrical operating parameters of generators and electric drives.Generally, currents from the milliampere range to the kiloampere rangehave to be measured, which requires a measuring range of five to sixmagnitudes.

The state of the art today is to measure magnetic fields, for example,of electric conductors, using magnetic-field sensors such as Hallsensors, bipolar magnetotransistors, magnetoresistive resistors, lateralmagneto-FET structures, etc. A particularly sensitive component is theso-called “lateral magnetotransistor” whose functioning is based on theasymmetrical current distribution between two bipolar transistors whichis generated by the magnetic field.

For currents in the milliampere range, even such components reach thelimits of their sensitivity due to the low magnetic fields, typically inthe μT range. In the related art, therefore, small magnetic fields areamplified by so-called “flux concentrators” which cause the magneticfields to be stronger at the location of the magnetic-field sensors bysuitably shaping the respective electric conductors or by means ofmagnetic circuits made of highly permeable materials.

SUMMARY OF THE INVENTION

The inventive device for sensing a magnetic field, the inventivemagnetic-field sensor and the inventive current sensor have theadvantage over the background art that flux-concentrating aids can bedispensed with, which saves costs and reduces the required installationspace. This is possible by increasing the sensitivity of the deviceaccording to the present invention. In this connection, the linearrelation between the measuring signal and the magnetic field to bemeasured is substantially maintained.

It is particularly advantageous that provision is made for a fourthmagnetic-field sensing means and for a fifth magnetic-field sensingmeans, an output variable of the second magnetic-field sensing meanscorresponding to an input variable of the fourth magnetic-field sensingmeans, and an output variable of the third magnetic-field sensing meanscorresponding to an input variable of the fifth magnetic-field sensingmeans. Thus, by varying the number of the cascade stages according tothe present invention, it is possible to obtain different sensitivities,as required, by the connection in cascade of magnetic-field sensors. Inthis context, it is particularly advantageous that differentmagnetic-field sensing means are implemented on a single chip.

Moreover, it is an advantage that the first magnetic-field sensing meansis a first lateral magnetotransistor, that the second magnetic-fieldsensing means is a second lateral magnetotransistor, and that the thirdmagnetic-field sensing means is a third lateral magnetotransistor. Inthis manner, the sensitivity of LMT (lateral magnetotransistor) sensorscan be increased according to the present invention by suitablycascading a plurality of such LMT components. By using the outputcurrent of one LMT element, i.e. according to the present invention, forexample, one of the two collector currents, as the input current, i.e.,according to the present invention, for example, as the emitter current,for a another LMT element, the asymmetry effect of the magnetic field onthe current distribution in the LMT can be used several times. In thiscontext, it is an advantage that an LMT sensor is already highlysensitive itself and therefore represents a good starting point for theoptimization described herein. Alternatively, the presented increase insensitivity can also be used for all other components working accordingto a similar principle, i.e., in which the values of two outputvariables are changed by a magnetic field.

It is also beneficial that the first output variable is a firstcollector current, that the second output variable is a second collectorcurrent, that the first input variable is the emitter current of thesecond lateral magnetotransistor, and that the second input variable isthe emitter current of the third lateral magnetotransistor. Thisadvantageously allows an increase in sensitivity, the relation betweenthe magnetic field and the measuring signal nevertheless being linearfor small magnetic fields.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a magnetic-field sensing means of the type of a lateralmagnetotransistor.

FIG. 2 is a schematic representation of a magnetic-field sensing means.

FIG. 3 shows an inventive arrangement of a plurality of magnetic-fieldsensing means.

DETAILED DESCRIPTION

In FIG. 1, a magnetic-field sensing means 1 is shown on the basis of alateral magnetotransistor. An important feature hereof is that there areone input variable and two output variables, the values of the outputvariables being essentially equal when a magnetic field 14 is absent inthe region of magnetic-field sensing means 1, and an asymmetry existingbetween a first output variable 12 and a second output variable 13 inthe presence of a magnetic field 14. The inventive arrangement ofmagnetic-field sensing means can be used for any magnetic-field sensingmeans having this fundamental property.

In FIG. 1, a lateral magnetotransistor 1, also abbreviated as LMT 1, isshown as an example of a magnetic-field sensing means 1. LMT 1 includesa first semiconductor substrate layer 5 which is, for example,negatively doped and a second semiconductor substrate layer 6 which is,for example, positively doped. Underneath first semiconductor substratelayer 5, that is, opposite of second semiconductor substrate layer 6,for example, a first metallization layer 7 is provided for bonding.First metallization layer 7 constitutes a vertical collector of LMT 1. Afirst semiconductor substrate region 8, which is, for example,negatively doped, is embedded in second semiconductor substrate layer 6.Adjacent to first semiconductor substrate region 8, a secondsemiconductor substrate region 9 and a third semiconductor substrateregion 10 are embedded in second semiconductor substrate layer 6, firstsemiconductor substrate region 8 being located in the middle betweensecond semiconductor substrate region 9 and third semiconductorsubstrate region 10. The second and third semiconductor substrateregions 9, 10 are doped in the same way as first semiconductor substrateregion 8. A first metallic contact 20, which constitutes the emittercontact of LMT 1, is disposed above first semiconductor substrate region8. A second metal contact 30, which constitutes a first lateralcollector of LMT 1, is located above second semiconductor substrateregion 9. A third metal contact 40, which constitutes a second lateralcollector of LMT 1, is arranged above third semiconductor substrateregion 10. A fourth metal contact 50, which constitutes a first baseterminal of LMT 1, is located next to second metal contact 30 on theopposite side of first metal contact 20. A fifth metal contact 60, whichconstitutes a second base terminal of LMT 1, is located next to thirdmetal contact 40 on the opposite side of first metal contact 20.

In LMT 1, a current flows from emitter region 8, i.e., from firstsemiconductor substrate region 8, vertically downward. In FIG. 1, thefirst current is provided with the reference numeral 11. First current11 corresponds to the input current to LMT 1 which is supplied via theemitter terminal. During operation, collector terminals 30, 40 are tiedto the same potential and a second current 12 arises from emitter region8 to first collector region 9, i.e., to second semiconductor substrateregion 9 and, moreover, a third current 13 arises from emitter region 8to second collector region 10, i.e., to third semiconductor substrateregion 10. According to the present invention, first current 11 iseither completely divided into second and third currents 12, 13, or apart of first current 11 flows to vertical collector 7. The first caseis relevant especially when no vertical collector 7, which is alsoreferred to as backside collector 7, is provided. In the second case,first current 11 is not completely divided into second and third current12, 13, but a part of first current 11 flows to backside collector 7. Inthe ideal case, i.e., when there is no offset or when the offset iscompensated for with sufficient accuracy, second current 12 and thirdcurrent 13 are equal in the absence of magnetic field 14, i.e., when itdisappears. When a magnetic field 14 is present which has a componentpointing vertically into the image plane, a symmetry break occurs withregard to first and second currents 12, 13: one of the currents becomeslarger.

Without magnetic field 14, in the ideal case, the two collectors 30, 40are traversed by the same current. By an applied magnetic field 14lateral to the chip surface, the charge carriers are deflected to theleft or to the right due to the Lorenz force, depending on the directionof the magnetic field. In the Figure, a magnetic field 14 pointingvertically into the drawing plane results in that a higher current isapplied to first collector 30; therefore, second current 12 is largerthan third current 13, resulting in a relative unbalance of the twocurrents 12, 13. The current difference between first collector 30 andsecond collector 40 induced by magnetic field 14 is the measuringsignal. The greater this difference for a given magnetic field strength,the higher is the sensitivity of the device.

FIG. 2 is a schematic representation of an LMT 1, showing only an inputvariable, which corresponds to input current 11 and is now provided withreference numeral 100, a first output variable 110 and a second outputvariable 120.

FIG. 2 schematically shows an equivalent circuit diagram of LMT 1depicted in FIG. 1. To first output variable 110 there corresponds, forexample, first current 12, i.e., to the first collector current of LMT1. To second output variable 120 there corresponds, for example, secondcurrent 13, i.e., to the second collector current of LMT 1. To inputvariable 100 there corresponds, for example, first current 11, i.e., theemitter current of LMT 1. The substrate current to vertical collectorterminal 7, which is not necessarily required for the LMT principle, isnot drawn in. For the measurement of the magnetic field, it is importantfor the field to induce as high as possible a change in the collectorcurrents, in the example, the output variables 110, 120. The greaterthese change relative to the output variables 110, 120 flowing withoutmagnetic field, the better is it possible to measure even small magneticfields 14. Therefore, the sensitivity of an LMT element can be definedas the ratios η=(magnitude of the difference of output variables 110,120 while magnetic field 14 is applied)/(magnitude of the sum of outputvariables 110, 120 when magnetic field 14 disappears). If input variable100, i.e., for example, the input current at emitter 20, is assumed tobe divided into the two output variables 110, 120 without losses, thenit applies for an individual sensor element that:

First output variable 110=α* input variable 100

second output variable 120=(1−α) * input variable 100,

where in the ideally symmetrical case without magnetic field it appliesfor asymmetry factor α that: α=0.50.

In this context, α is dependent on the magnetic field, which is alsodenoted by the letter “B”. An asymmetry factor α which has been changedby the magnetic field is written as α(B). In the starting situationwithout magnetic field, it applies that α=α(0).

In the presence of a third substrate collector current, which is notdenoted by reference numerals, to vertical collector terminal 7, theproportion of the output variables, i.e., of lateral currents 110, 120,decreases according to the reduction of the third vertical current path,that is, not emitter current 11 but emitter current 11 minus thesubstrate current flowing to vertical collector 7 is taken as inputvariable 100. For an individual LMT element 1, measuring sensitivity ηis derived as

η=|2*α(B)−1| for α(0)=0.50

In the presence of a magnetic field 14, α increases or decreases,depending on the field direction, with the component of magnetic field14 that runs parallel to the surface of LMT 1. FIG. 3 shows an inventivearrangement of magnetic-field sensing means. All in all, a firstmagnetic-field sensing means 101, a second magnetic-field sensing means201, a third magnetic-field sensing means 301, a fourth magnetic-fieldsensing means 401, and a fifth magnetic-field sensing means 501 areshown. The input variable of first magnetic-field sensing means 101 isprovided with reference numeral 100. First magnetic-field sensing means101 has first output variable 10 and second output variable 120 as theoutput variables. Second magnetic-field sensing means 201 has the inputvariable, which is provided with reference numeral 200, and, as outputvariables, first output variable 210 and second output variable 220 ofsecond magnetic-field sensing means 201. Accordingly, thirdmagnetic-field sensing means 301 has an input variable, which isprovided with reference numeral 300. Third magnetic-field sensing means301 has a first output variable 310 and a second output variable 320 asthe output variables. The fourth magnetic-field sensing means has aninput variable, which is provided with reference numeral 400, as well asa first output variable provided with reference numeral 410 and a secondoutput variable provided with reference numeral 420. Fifthmagnetic-field sensing means 501 has an input variable, which isprovided with reference numeral 500, as well as a first output variableprovided with reference numeral 510 and a second output variableprovided with reference numeral 520. According to the present invention,first output variable 110 of first magnetic-field sensing means 101 isused as input variable 200 to second magnetic-field sensing means 201,and second output variable 120 of first magnetic-field sensing means 101is used as input variable 300 to third magnetic-field sensing means 301.When first, second and third magnetic-field sensing means 101, 201, 301produce an essentially equal relative unbalance of their outputvariables 110 and 120, and 210 and 220, and 310 and 320, respectively,as a function of an applied magnetic field 14, then the relativeunbalance between first output variable 210 of the second magnetic-fieldsensing means and second output variable 320 of the third magnetic-fieldsensing means is greater than the unbalance between first outputvariable 110 of first magnetic-field sensing means 101 and second outputvariable 120 of first magnetic-field means 101. Given the same appliedmagnetic field 14, therefore, the sensitivity of the system composed offirst magnetic-field sensing means 101 together with secondmagnetic-field sensing means 201 and third magnetic-field sensing means301 is greater than the sensitivity of the first magnetic-field sensingmeans alone. Thus, according to the present invention, the possibilityarises to cascade magnetic-field sensing means by adding furthermagnetic-field sensing means 201, 301, 401, 501, starting from firstmagnetic-field sensing means 101. In such a cascading arrangement, firstmagnetic-field sensing means 101 alone represents, as it were, the firststage of the cascade, second magnetic-field sensing means 201 and thirdmagnetic-field sensing means 301 constitute the second stage of thecascade; first magnetic-field sensing means 101, second magnetic-fieldsensing means 201 and third magnetic-field sensing means 301 togetherforming a two-stage cascade 70. Accordingly, all five magnetic-fieldsensing means 101, 201, 301, 401, 501 constitute a three-stage cascade80 of magnetic-field sensing means. According to the present invention,an arbitrary number of cascade stages can be provided. For the sake ofsimplicity, only the first three cascade stages are described by way ofexample.

Via the number of cascade stages, it is possible to obtain differentsensitivities of the device according to the present invention asrequired. The connection in cascade of lateral magnetotransistors 101,201, 301, 401, 501 can be implemented monolithically, that is, on asingle chip. An LMT cascade chip, as an example for a cascade ofmagnetic-field sensing means, is able to cover a very large measuringrange for which otherwise a combination of different sensor elementswould have to be used according to the related art. In the case of sucha device featuring different sensor elements, which cover differentsensitivity ranges, each of these individual sensors would have to beadapted to different measuring ranges by control, for example, via anevaluation IC. This would be carried out, for example, by differentlyamplifying the signal to be evaluated. However, this would not improvethe signal-to-noise ratio. According to the present invention, a greatadvantage of the cascading of magnetic-field sensing means proposed bythe present invention is that the appropriate sensitivity range of thesensor can be selected and evaluated for each measuring signal strength.

According to the present invention, a cascade of a plurality ofmagnetic-field sensing means or of a plurality of LMT components servesto increase the measuring sensitivity of a device according to thepresent invention. The effect of magnetic field 14 is amplified in thatthe output current of an LMT element that is changed by magnetic field14 is used in each case as the input current for the next LMT elementand is consequently subject to the effect of the magnetic field again.In an n-fold cascade of magnetic-field sensing means, measuringsensitivity η is calculated from the current difference of the two lastcascade elements of the magnetic-field sensing means of the cascade asfollows:

η_(n):η₁=|α(B)^(n)−(1−α(B))^(n)|/|α(0)^(n)+(1−α(0))^(n)

The increase in sensitivity obtained by the cascade can be bestdescribed as the ratio of the sensitivities between the n-fold cascade(η_(n)) and the sensitivity of a single element (η₁):

η_(n):η₁=|α(B_(z))^(n)−(1−α(B_(z)))^(n)|/{[α(0)^(n)+(1−α(0))^(n)]·|2α(B_(z))−1|

If, in the ideal case, α(0) is assessed to be 0.50, it follows that:

η_(n):η_(n1)=2^(n−1)*|α(B)^(n)−(1−α(B))^(n)|/|2α(B)−1|

For small magnetic fields, i.e., α is approximately equal to 0.50, thesensitivity increases linearly with the number of cascade stages. Themore magnetic-field sensing means are connected in cascade or thegreater magnetic field 14, the faster increases sensitivity η_(n). Theloss of the linear relation between the measuring signal and themagnetic field for a cascade having more than two stages appears to be adisadvantage of the cascade connection. However, the non-linearity can,on one hand, be allowed for in the evaluation of the measuring signal;on the other hand, the non-linearity comes to the forefront only when astrongly deviates from 0.50, that is, for high magnetic fields.According to the present invention, however, the object of the presentinvention is primarily to increase the measuring sensitivity for smallfields so that the cascade connection can be used, in particular, in therange of a approximately equal to 0.50. In this range, the inventivecascade connection of magnetic-field sensing means behaves linearlybecause it results for α=0.50 that η_(n)=n*η₁, the sensitivityincreasing linearly with the number n of cascade stages.

The cascade connection according to the present invention can beimplemented both with separate LMT elements and on a chip by linkingindividual LMT cells in a suitable manner. Control can take place, forexample, via an ASIC. It is also possible to tap the measuring signal atdifferent cascade stages so that the cascade depth to be evaluated canbe selected as a function of the requested sensitivity. Moreover, theLMT operating points of different cascade stages can be setindependently of each other, for example, via the selection of therespective base current, whereby offset or temperature effects canpossibly be compensated for. Because it is in principle possible to seteach operating point of the interconnected elements separately, thedevice according to the present invention can be combined with differentcontrol or evaluation concepts in an extremely flexible manner.

For a connection in cascade, it is not only conceivable to use thecollector current as output variable and the emitter current as inputvariable but it is also conceivable to use two emitters as outputs andone collector as input of the following element. The third possibilityof using the output current as base input for the following elementpromises an even higher increase in sensitivity.

Currently, LMT elements typically have an edge length of approximately50 to 100 μm on a chip. Therefore, such elements can easily be cascadedby arranging the LMT elements in blocks, side by side, or in a differentalignment on a chip. In this context, magnetic field 14 to be measuredis assumed to be approximately equal at the locations of the various LMTelements situated on the chip, that is, magnetic field 14 is homogeneousover the chip region which is used for the measurement. This is anabsolutely plausible assumption for the indicated dimensions of thesensor elements.

What is claimed is:
 1. A device for sensing a magnetic field,comprising: a first magnetic-field sensing device; a secondmagnetic-field sensing device; and a third magnetic-field sensingdevice, wherein: a first output variable of the first magnetic-fieldsensing device is provided as a first input variable, a second outputvariable of the first magnetic-field sensing device is provided as asecond input variable, the first input variable is provided as an inputvariable for the second magnetic-field sensing device, and the secondinput variable is provided as an input variable for the thirdmagnetic-field sensing device.
 2. The device as recited in claim 1,further comprising: a fourth magnetic-field sensing device; and a fifthmagnetic-field sensing device, wherein: an output variable of the secondmagnetic-field sensing device corresponds to an input variable of thefourth magnetic-field sensing device, and an output variable of thethird magnetic-field sensing device corresponds to an input variable ofthe fifth magnetic-field sensing device.
 3. The device as recited inclaim 1, wherein: the first magnetic-field sensing device includes afirst lateral magnetotransistor, the second magnetic-field sensingdevice includes a second lateral magnetotransistor, and the thirdmagnetic-field sensing device includes a third lateralmagnetotransistor.
 4. The device as recited in claim 3, wherein: thefirst output variable includes a first collector current, the secondoutput variable includes a second collector current, the first inputvariable includes an emitter current of the second lateralmagnetotransistor, and the second input variable is an emitter currentof the third lateral magnetotransistor.
 5. The device as recited inclaim 3, wherein: the first output variable includes one of a firstemitter current and a first emitter voltage, the second output variableincludes one of a second emitter current and a second emitter voltage,the first input variable includes one of a collector current and acollector voltage of the second lateral magnetotransistor, and thesecond input variable includes one of a collector current and acollector voltage of the third lateral magnetotransistor.
 6. The deviceas recited in claim 2, wherein: the first magnetic-field sensing device,the second magnetic-field sensing device, the third magnetic-fieldsensing device, the fourth magnetic-field sensing device, and the fifthmagnetic-field sensing device are provided in a monolithicallyintegrated form.
 7. The device as recited in claim 1, furthercomprising: an evaluation circuit, the evaluation circuit evaluating oneof the following sets of variables as a function of the magnetic field:the first output variable and the second output variable of the firstmagnetic-field sensing device, and an output variable of the secondmagnetic-field sensing device and an output variable of the thirdmagnetic-field sensing device.
 8. The device as recited in claim 1,wherein: the device is included in a magnetic-field sensor.
 9. Thedevice as recited in claim 1, wherein: the device is included in acurrent sensor.